The present invention relates to an airfoil for a bucket of a stage of a gas turbine and particularly relates to a stage two bucket airfoil having an optimized number, location, style and size of cooling holes for flowing a cooling medium, e.g., air, through the airfoil.
Many different types, numbers and locations of passages for flowing a cooling medium, e.g., air, through an airfoil of a turbine bucket for cooling the airfoil have been proposed and constructed. Where air is used as the cooling medium, it will be appreciated that the air is derived from the compressor and therefore results in a debit to the overall efficiency of the turbine. In prior cooling configurations for turbine buckets, compressor discharge air is supplied to the airfoil through cooling passages formed integrally within the bucket. Insufficient cooling, however, affects bulk creep part life which in turn limits the life of the part to a predetermined number of hours of turbine operation. Accordingly, a more effective cooling scheme which decreases the bulk temperature of the bucket and increases the bucket's bulk creep life is deemed necessary.